Kidney function tests are common lab tests used to evaluate how well the kidneys are working. Such tests include:
- BUN (Blood urea nitrogen)
- Creatinine – blood
- Creatinine clearance
- Creatinine – urine
BUN – blood test
Blood urea nitrogen
BUN stands for blood urea nitrogen. Urea nitrogen is what forms when protein breaks down.
A test can be done to measure the amount of urea nitrogen in the blood.
How the Test is Performed
A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.
How to Prepare for the Test
Many medicines can interfere with blood test results.
- Your health care provider will tell you if you need to stop taking any medicines before you have this test.
- DO NOT stop or change your medicines without talking to your provider first.
How the Test will Feel
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
Why the Test is Performed
The BUN test is often done to check kidney function.
Normal Results
The normal result is generally 6 to 20 mg/dL.
Note: Normal values may vary among different labs. Talk to your doctor about your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Higher-than-normal levels may be due to:
- Congestive heart failure
- Excessive protein levels in the gastrointestinal tract
- Gastrointestinal bleeding
- Hypovolemia (dehydration)
- Heart attack
- Kidney disease, including glomerulonephritis , pyelonephritis, and acute tubular necrosis
- Kidney failure
- Shock
- Urinary tract obstruction
Lower-than-normal levels may be due to:
- Liver failure
- Low protein diet
- Malnutrition
- Over-hydration
Considerations
For people with liver disease , the BUN level may be low even if the kidneys are normal.
Creatinine blood test
Serum creatinine
The creatinine blood test measures the level of creatinine in the blood. This test is done to see how well your kidneys are working.
Creatinine can also be measured with a urine test.
How the Test is Performed
A blood sample is needed .
How to Prepare for the Test
The health care provider may tell you to temporarily stop taking certain medicines that can affect the test. These medicines include:
- Cimetidine, famotidine, and ranitidine
- Certain antibiotics, such as trimethoprim
Tell your provider about all the medicines you take.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
Creatinine is a chemical waste product of creatine. Creatine is a chemical made by the body and is used to supply energy mainly to muscles.
This test is done to see how well your kidneys work. Creatinine is removed from the body entirely by the kidneys. If kidney function is not normal, the creatinine level in your blood will increase. This is because less creatinine is released through your urine.
Normal Results
A normal result is 0.7 to 1.3 mg/dL for men and 0.6 to 1.1 mg/dL for women.
Women usually have a lower creatinine level than men. This is because women usually have less muscle mass than men. Creatinine level varies based on a person’s size and muscle mass.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
A higher than normal level may be due to:
- Blocked urinary tract
- Kidney problems, such as kidney damage or failure, infection, or reduced blood flow
- Loss of body fluid (dehydration)
- Muscle problems, such as breakdown of muscle fibers ( rhabdomyolysis )
- Problems during pregnancy, such as seizures caused by eclampsia or high blood pressure caused by preeclampsia
A lower than normal level may be due to:
- Conditions involving the muscles and nerves that lead to decreased muscle mass
- Malnutrition
There are many other conditions for which the test may be ordered, such as high blood pressure, diabetes, or medicine overdose. Your provider will tell you more, if needed.
Risks
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Creatinine clearance test
The creatinine clearance test helps provide information about how well the kidneys are working. The test compares the creatinine level in urine with the creatinine level in blood.
How the Test is Performed
This test requires both a urine sample and blood sample . You will collect your urine for 24 hours and then have blood taken. Follow instructions exactly. This ensures accurate results.
How to Prepare for the Test
Your health care provider may ask you to temporarily stop any medicines that may affect the test results. These include antibiotics and stomach acid medicines. Be sure to tell your provider about all the medicines you take.
DO NOT stop taking any medicine before talking to your provider.
How the Test will Feel
The urine test involves only normal urination. There is no discomfort.
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
Creatinine is a chemical waste product of creatine. Creatine is a chemical the body makes to supply energy, mainly to muscles.
By comparing the creatinine level in urine with the creatinine level in blood , this test estimates the glomerular filtration rate (GFR) . GFR is a measure of how well the kidneys are working, especially the kidneys’ filtering units. These filtering units are called glomeruli.
Creatinine is removed, or cleared, from the body entirely by the kidneys. If kidney function is abnormal, creatinine level increases in the blood because less creatinine is released through the urine.
Normal Results
Clearance is often measured as milliliters per minute (mL/min) or milliliters per second (mL/s). Normal values are:
- Male: 97 to 137 mL/min (1.65 to 2.33 mL/s).
- Female: 88 to 128 mL/min (14.96 to 2.18 mL/s).
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal results (lower than normal creatinine clearance) may indicate:
- Kidney problems, such as damage to the tubule cells
- Kidney failure
- Too little blood flow to the kidneys
- Damage to the filtering units of the kidneys
- Loss of body fluids (dehydration)
- Bladder outlet obstruction
- Heart failure
Risks
Risks of the test involve the blood draw process.
Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Creatinine urine test
Urine creatinine test
The creatinine urine test measures the amount of creatinine in urine. This test is done to see how well your kidneys are working.
Creatinine can also be measured by a blood test.
How the Test is Performed
After you provide a urine sample, it is tested in the lab. If needed, your doctor may ask you to collect your urine at home over 24 hours . Your health care provider will tell you how to do this. Follow instructions exactly so that the results are accurate.
How to Prepare for the Test
Your health care provider may tell you to temporarily stop taking certain medicines that may affect test results. Be sure to tell your provider about all the medicines you take. These include:
- Antibiotics such as cefoxitin or trimethoprim
- Cimetidine
DO NOT stop taking any medicine before talking to your provider.
How the Test will Feel
The test involves only normal urination. There is no discomfort.
Why the Test is Performed
Creatinine is a chemical waste product of creatine. Creatine is a chemical the body makes to supply energy, mainly to muscles.
This test is done to see how well your kidneys work. Creatinine is removed by the body entirely by the kidneys. If kidney function is not normal, creatinine level in your urine decreases.
This test can be used for the following:
- To evaluate how well the kidneys are working
- As part of the creatinine clearance test
- To provide information on other chemicals in the urine, such as albumin or protein
Normal Results
Urine creatinine (24-hour sample) values can range from 500 to 2000 mg/day. Results depend on your age and amount of lean body mass.
Another way of expressing the normal range for test results is:
- 14 to 26 mg per kg of body mass per day for men
- 11 to 20 mg per kg of body mass per day for women
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal results of urine creatinine may be due to any of the following:
- High meat diet
- Kidney problems, such as damage to the tubule cells
- Kidney failure
- Too little blood flow to the kidneys, damage to filtering units
- Kidney infection (pyelonephritis)
- Muscle breakdown ( rhabdomyolysis ), or loss of muscle tissue ( myasthenia gravis )
- Urinary tract obstruction
Risks
There are no risks with this test.
